EDIT: Changed to solved, bad thermostat for sure
Truck was idling rough again, so I checked for any codes to see if anything can help me further troubleshoot this current issue (replacing spark plugs because I could not find any vacuum leaks) Instead of getting a misfire code or etc. I see a P0128 - Does this mean that my thermostat is starting to stay in the open position? It's running 10-20 degrees cooler than normal., depending on if it's idling or driving. Look at my screenshot of Dash Command below for example and you'll see it's about 12 degrees cooler than normal when driving.
EDIT: Just delved a bit more into this and yeah, going to be repacing the thermostat. The old site,(TV) is a great archive:
""....T-stat was sticking. Replace it now or you'll be replacing it later. I should add, the P0128 doesn't get set after just "one time" of operating temps below thermostat regulated temps- it has to do it so many times in so many driving cycles with a whole bunch of criteria to be met:
DTC P0128
Circuit Description
An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) for engine control and as an enabling criteria for some diagnostics.
-The air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.
-This diagnostic trouble code (DTC) will only run once per ignition cycle within the enabling conditions.
-If the engine coolant fails to reach a preset target temperature before a calculated air flow is accumulated, DTC P0128 will set.
-Conditions for Running the DTC
DTCs P0105, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0125, P0130, P0131, P0132, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0325, P0336, P0420, P0440, P0442, P0446, P0452, P0453, P0480, P0502, P0503, for automatic transmission only, and P1441 are not set.
The engine has run more than 30 seconds and less than 20 minutes.
The minimum intake air temperature (IAT) is more than -7°C (19°F).
The engine coolant temperature at start up is less than 65°C (149°F).
-Conditions for Setting the DTC
The average air flow is more than 20 g/s.
The vehicle has traveled more than 2.4 km (1.5 mi) over 40 km/h (25 mph).
Enough air flow has entered the engine and the engine coolant temperature has not risen to 80°C (176°F) for 30 seconds.
-Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.
The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records.
-Conditions for Clearing the MIL or DTC
The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
Use a scan tool in order to clear the DTCs.
Diagnostic Aids
A DTC P0128 is designed to detect a faulty thermostat.
A fault in the IAT would certainly set a P0112 and have to indicate 20 test failures in a 20 second period to set that DTC.""
Truck was idling rough again, so I checked for any codes to see if anything can help me further troubleshoot this current issue (replacing spark plugs because I could not find any vacuum leaks) Instead of getting a misfire code or etc. I see a P0128 - Does this mean that my thermostat is starting to stay in the open position? It's running 10-20 degrees cooler than normal., depending on if it's idling or driving. Look at my screenshot of Dash Command below for example and you'll see it's about 12 degrees cooler than normal when driving.
EDIT: Just delved a bit more into this and yeah, going to be repacing the thermostat. The old site,(TV) is a great archive:
""....T-stat was sticking. Replace it now or you'll be replacing it later. I should add, the P0128 doesn't get set after just "one time" of operating temps below thermostat regulated temps- it has to do it so many times in so many driving cycles with a whole bunch of criteria to be met:
DTC P0128
Circuit Description
An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) for engine control and as an enabling criteria for some diagnostics.
-The air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.
-This diagnostic trouble code (DTC) will only run once per ignition cycle within the enabling conditions.
-If the engine coolant fails to reach a preset target temperature before a calculated air flow is accumulated, DTC P0128 will set.
-Conditions for Running the DTC
DTCs P0105, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0125, P0130, P0131, P0132, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0325, P0336, P0420, P0440, P0442, P0446, P0452, P0453, P0480, P0502, P0503, for automatic transmission only, and P1441 are not set.
The engine has run more than 30 seconds and less than 20 minutes.
The minimum intake air temperature (IAT) is more than -7°C (19°F).
The engine coolant temperature at start up is less than 65°C (149°F).
-Conditions for Setting the DTC
The average air flow is more than 20 g/s.
The vehicle has traveled more than 2.4 km (1.5 mi) over 40 km/h (25 mph).
Enough air flow has entered the engine and the engine coolant temperature has not risen to 80°C (176°F) for 30 seconds.
-Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.
The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records.
-Conditions for Clearing the MIL or DTC
The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
Use a scan tool in order to clear the DTCs.
Diagnostic Aids
A DTC P0128 is designed to detect a faulty thermostat.
A fault in the IAT would certainly set a P0112 and have to indicate 20 test failures in a 20 second period to set that DTC.""
Last edited:
